Re: DBWn performs batched (multiblock) writes to improve efficiency

I definitely have seen multiblock pwrites in dbwr's truss/strace output (you
can also see write coalescing from dbwr trace if you set _dbwr_tracing to 8.
Note that it generates quite a lot of trace so don't set it in production).

Of course the blocks to be written written to disk have to be adjacent in
order to use a multiblock write.

Do a full delete on a test table for example, you should see some multiblock
writes then. Whether adjacent blocks' corresponding dirty buffers are
written to disk using a multiblock or single block write, is dependent on
dbwr's internal batch composition algorithm, LRU list contents, "hotness" of
a block and incremental checkpoint agressiveness, so it's nothing unusual if
adjacent dirty blocks are written to disk on different times with different
write calls...

> From oracle 9i database concepts manual, I saw note:> In all cases, DBWn performs batched (multiblock) writes to improve
efficiency. The number of blocks written in a multiblock write varies by
operating system.
>> link: